The present invention is directed to a method for generating digital imaging data for an imaging unit, in which digital imaging data are defined from a signature of input image data, in that a section of the signature corresponding to the imaging format of the imaging unit is processed into a raster image by a raster image processor. In addition, the present invention is directed to a raster image processor having a raster-image-processor program, for implementing the method according to the present invention.
In the graphics industry, various imaging devices exist which can be used to selectively modify the properties or the structure of a surface area, directly at the machine level, in accordance with digital imaging data, in order to prepare a printing form for a specific printing process. In principle, one distinguishes between so-called computer-to-press systems and computer-to-plate systems: In a computer-to-press system, a printing form or a printing-form precursor is directly imaged in a print unit of a printing press on the basis of digital imaging data. A print unit of this kind, which encompasses an imaging unit, is also described as a direct on-press imaging print unit. In a computer-to-plate system, a printing form or a printing-form precursor is imaged independently of a printing press, in a prepress unit on the basis of digital imaging data. Such a prepress unit can also be described as a printing-form imagesetter. However, in computer-to-press and computer-to-plate systems, the imaging results of a signature (of a sheet) of input image data deviate in size from one another.
When a computer-to-plate system is used, in principle, a complete printing form, i.e., an entire area including the non-printing regions, is imaged. Consequently, this means that all geometric specifications pertaining to the signature (of the imposition sheet) refer to the complete printing form. In contrast, in direct on-press imaging print units, in principle, it is only the maximum printing format (the maximally imageable surface of the printing form) that can be imaged. However, since the maximum printing format is always only a true partial area of a printing form, a record of digital imaging data for a computer-to-press system is always larger than a record of digital imaging data for a computer-to-plate system. Therefore, digital computer-to-plate imaging data cannot be used on a direct on-press imaging print unit without adaptations being made. In the event of a job order change—even within one format class of printing presses—from a conventional printing press (for example a Speedmaster 74 press of Heidelberger Druckmaschinen AG) to a direct on-press imaging printing press (for example of a Speedmaster 74 DI press of Heidelberger Druckmaschinen AG), it is disadvantageous that the signature to be imaged must be completely recreated, because of the different geometries mentioned above. A further restriction is seen in that information pertaining to the geometry of a signature for imaging in a direct on-press imaging print unit cannot be used directly in a print-finishing unit, but, at best, only after adaptations are made.
It should also be mentioned that, increasingly, printing-form imagesetters come equipped with supplementary devices, such as automatic printing-form cutting dies, so that the imageable format can be smaller than the complete printing form surface. Consequently, the maximum sizes of the records of digital imaging data differ among various printing-form imagesetters, so that it is not possible to exchange digital imaging data without making adaptations to the particular computer-to-plate system.
In present-day raster image processors for direct on-press imaging print units or for direct on-press imaging printing presses, there are limitations to the processing of very large records of digital imaging data: Typical reactions of the raster image processor are an abnormal termination of the processing, an automatic scaling of the imaging data, or an arbitrary trimming to a maximum imaging format of the direct on-press imaging print unit or of the direct on-press imaging printing press. All of these reactions lead to an unsuitable result. As a rule, a scaling in unacceptable, since the size of the product to be printed inevitably changes. An automatic trimming is likewise unsuitable, since, in computer-to-plate systems, this step is dependent on the defined imaging zero reference point, typically at a plate corner, while in computer-to-press systems, the printing form is always centrically positioned. Because of the different reference points resulting therefrom, the information to be printed is also cropped, making the result unusable.
The European Patent Application EP 1 258 828 A2, related to U.S. Patent Application No. 2002/0171871, both of which are hereby incorporated by reference herein, describes a raster image processing system. In this system, output pages are generated for a number of different output units, such as printers, proofers, filmsetters, imagesetters, direct on-press imaging systems and the like. Page raster data and press sheet templates are processed into output pages, the press sheet templates including information on position, orientation, image area and offset parameters. In a raster image processor, these data are extracted, so that the press sheet templates can be used for the image data. The press sheet templates can be displayed, defined, and modified by the user, in particular on a monitor. The information regarding the location where the press sheet is to be positioned can be used for output on different printing formats. Generally usable press sheet templates can be stored. The disadvantage of the described processing system is, inter alia, that sections are only defined for imaging after the image data have already been fully rasterized. Therefore, only output units having the same resolution can be used.